#include <stdio.h> 

int main()
{
	freopen("test.in", "r", stdin);
	freopen("test.out", "w", stdout);
	int n = 0;
	long long sum = 0;
	
	scanf("%d", &n);
	for ( int i = 1; i <= n; i++ ) {
		sum += i;
	}
	printf("%d", sum);
	fclose(stdin);
	fclose(stdout);
	return 0;
}
